SPI Moving Itself

Anyone have the experience of setting a SPI with the TGP from high altitude and then on the way into the target having it move suddenly all on its own? I've had this happen several times running a particular mission (Maple Flag TAC14) and so have others I think. I wonder if it's a bug or something I've done. I marked the target and then came down to the deck and every time running in I can watch the wedding cake suddenly move on my TAD. I didn't touch a control. I have some track files but they're huge. Can the SPI just get lost when you're too low to the ground? I understand the use of the laser in marking them at a high slant angle but this isn't the case and anyways all that will do it put it in the right spot, not prevent it from moving.

Screenshots here

http://forums.eagle.ru/showthread.php?t=143448&page=2

As per my reply in the other thread, if your SPI generator moves to focus on a different position of course your SPI will change to match it.

Your problem is largely caused by poor procedures, specifically relying on the TGP as SPI generator rather than using waypoints/mark points.

Try switching the Track mode from area or point to inertia, then create your SPI. That way it will stay on the place you want it to, even when you loose sight to your target due to terrain masking or Gimbal limit. Might not be the correct procedure but it works for me :)

But of course Eddie is right make a markpoint and slew to that, that's the way to go :)

There are a number of things that can cause you to lose your SPI track. In my experience it's usually terrain masking or a lot of maneuvers enroute to that point. I've also noticed that if I don't allow my INS to align (fully) before turning the TGP on, things can get wacky. It is a matter that requires your troubleshooting and may be a procedural gap.

Eddie, with all due respect to your great level of knowledge on DCS, I don't agree with the fact that a waypoint/markpoint should have to be set for every target. I rarely do that and I operate just fine.

On a side note, I've found that sometimes when my SPI fades off point it's actually just my TGP view, so if I slave all to SPI again, everything comes right.

Try switching the Track mode from area or point to inertia, then create your SPI. That way it will stay on the place you want it to, even when you loose sight to your target due to terrain masking or Gimbal limit. Might not be the correct procedure but it works for me :)

How does one switch to that "inertia" mode?

Eddie, with all due respect to your great level of knowledge on DCS, I don't agree with the fact that a waypoint/markpoint should have to be set for every target. I rarely do that and I operate just fine

That's fine, but the USAF do. It's real world procedure, and for very good reason. In fact when employing IAMs, using steer point as SPI generator is mandatory.

Most of these issues stem from one simple fact, people often seem not to understand the the SPI is not a point you designate, it is a constantly updated position in 3d space which is produced by whichever sensor/system you set as SPI generator. This is why using a non fixed position (ie steer point) as SPI generator can have undesirable effects.

While in sim those undesirable effects aren't a big thing for some, in reality it's how you end up dropping a weapon on friendlies/civilians.

Most of these issues stem from one simple fact, people often seem not to understand the the SPI is not a point you designate, it is a constantly updated position in 3d space which is produced by whichever sensor/system you set as SPI generator.

Aha. So that's what I'm not getting. I thought a SPI was something you designate and once you've done that it stays put. If you want to do that I guess the correct thing to do would be make a Markpoint. In this case I'm getting terrain in the way of the TGP and its moving the SPI around to correspond with where it's aiming and intersects the ground, correct?

Indeed. One of the many reasons the TGP isn't a good tool to be using at low level.

Is the idea for the mark point to have a general area where your TGP can locate then slave the weapon of choice to use for attack?

Assuming a static point target, the WP/MP should be where you want the weapon to impact. The only time the TGP would have to factor in to the equation is if you're employing LGB at that point, unless of course you specifically require the TGP on target to provide rapid BDA etc. Moving targets would of course require TGP/LGB or Maverick.

The idea is that you employ the weapon on to a fixed position which is always using the same switch flow, i.e. by always using the steer point as SPI generator when employing ordnance you vastly reduce the risk of employing a weapon while having the incorrect SPI generator selected resulting in the weapon going elsewhere than intended.

Naturally, this applies to medium altitude engagements. For low altitude engagement things are different of course, as you'd be operating almost exclusively visually rather than performing system deliveries.

Interesting thread. :thumbup:

Regarding the original question, since it was not brought up yet, the dreaded gimbal roll tends to happen every now and then when the aircraft maneuvers a lot without resetting/boresighting the TGP, but AFAIK it reads GIMB ROLL on the TGP so I guess that's not what happened, SharpeXB, or is it?

In any case, if that happens and when the TGP is set as SPI generator (check HUD, lower left column), slaving all to SPI won't do anything since wherever the TGP looks is the SPI. :smartass:

This is why using a non fixed position (ie steer point) as SPI generator can have undesirable effects.

Just a quick question: the part I marked in bold, that should have read TGP or maybe TDC, shouldn't it?

Try switching the Track mode from area or point to inertia, then create your SPI. That way it will stay on the place you want it to, even when you loose sight to your target due to terrain masking or Gimbal limit. Might not be the correct procedure but it works for me :)

Inertia mode? Whats that if you don't mind me asking? Is this the mode where you just do a short aft on the TMS? If it is what's the difference between that mode and area mode?

That's it. Area / Point mode will try to stay on a spot you lock no matter how much you manoeuvre, the downside being that if your target is masked (by a mountain for instance) it will become glued to the obstacle. In inertia mode your TGP does not lock on anything.

Just a quick question: the part I marked in bold, that should have read TGP or maybe TDC, shouldn't it?

It should, yes.

Inertia mode? Whats that if you don't mind me asking? Is this the mode where you just do a short aft on the TMS? If it is what's the difference between that mode and area mode?

exactly. TMS short aft will switch to INR tracking mode. What I do is the following:

lock on desired target in point mode, laser on to get an accurate distance reading, TMS aft short to switch to INR mode and make SPI via TMS fwd long.

That way, your SPI wont jump whenever the TGP camera loses line of sight for a second, such as terrain masking or excessive maneneuvering. You can either use my method, or do as Eddie suggests and make a markpoint where you slew sensors to for SPI.

The way I see it, both methods are doing the same thing, the point is that instead of fixating your sensors on a given point in 3D-space (such as in AREA or POINT track, which will 'jump' as soon as you have terrain masking, because the camera now sees a new area or point as soon as a hill comes into line of sight and fixates on the new object now).

In INR (or using a markpoint) you now fix your sensors to a place on the ground (no matter of masking), defined my 2D coordinates + elevation.

Mark points are just what they say they are. They are a point marked in space/on the ground that can be used as a reference for other sensors to be aimed at, or as a point around which to orbit etc.

Just like pushing a digital pin into a map.

Once you have the mark point established, you can use it in lots of ways.

Good points Eddie, I didn't know that was SOP.

One way I do often use mark points is the Zmark. I'll make my initial attack (which automatically makes a mark point labeled Z), then if I have trouble returning sensors to that area I'll switch to mark and select Z. In low altitude engagements (gun runs definitely) I almost always use my Zmark to keep SA. I'm going to rework my TTPs for an initial mark and see if it works for me.

exactly. TMS short aft will switch to INR tracking mode. What I do is the following:

 

lock on desired target in point mode, laser on to get an accurate distance reading, TMS aft short to switch to INR mode and make SPI via TMS fwd long.

I see, but it would be a lot easier just putting down a mark point and naming it something like tanks ect. I think I'd start to get confused if I did it your way, but maybe it's just getting used to it that way.

It should, yes.

Thanks for confirmation. I thought I might have misunderstood something, but now it all makes sense. :thumbup:

exactly. TMS short aft will switch to INR tracking mode. What I do is the following:

 

lock on desired target in point mode, laser on to get an accurate distance reading, TMS aft short to switch to INR mode and make SPI via TMS fwd long.

 

That way, your SPI wont jump whenever the TGP camera loses line of sight for a second, such as terrain masking or excessive maneneuvering. You can either use my method, or do as Eddie suggests and make a markpoint where you slew sensors to for SPI.

 

The way I see it, both methods are doing the same thing, the point is that instead of fixating your sensors on a given point in 3D-space (such as in AREA or POINT track, which will 'jump' as soon as you have terrain masking, because the camera now sees a new area or point as soon as a hill comes into line of sight and fixates on the new object now).

 

In INR (or using a markpoint) you now fix your sensors to a place on the ground (no matter of masking), defined my 2D coordinates + elevation.

Actually when I set this SPI in question I was in INR Point mode and it still got reset when I moved behind terrain.

It would do. Using inertial rates at all when employing ordnance is a bad idea. INR is really a fallback mode used when either the pod can't obtain and optical track or looses one (neither of which happen in DCS sadly). And the LASER won't actually fire when using INR either, the source of many an auto lase failure amongst newbies in my experience.

And your SPI didn't get "reset" it just moved. Semantics, maybe, but those kind of comments/thoughts help reinforce the idea that a SPI is a fixed point that is designated once, which it isn't. ;)

strange, for me it always worked in INR. Youre sure you set SPI after you switched to INR? but then again, its pointless, as Eddie said, markpoints are our friends :)

Here's a video of the mission. Embellished slightly... :)

Right at 3:45 you can see the wedding cake of the TAD in a different spot than it was before I went behind the hill. Then as I go over the ridge it goes back to where it was, it's tracking where the TGP LoS hits the terrain.